Study of degumming and neutralization units
a
Oliveira, Sara; Alves, Sebastião ; Carvalho, Renato a b
b
Department of Chemical Engineering, Instituto Superior Técnico, Technical University of Lisbon, Lisbon, Portugal
Technological Development Department, Iberol – Sociedade Ibérica de Biocombustíveis e Oleaginosas, S.A , Alhandra, Portugal
Abstract The purpose of this work was the study of the pre-treatment processes of vegetable oils existing in Iberol to produce biodiesel (the water degumming step and the chemical degumming and neutralization unit), to identify factors that could be improved and suggest hypotheses of optimization. To meet this objective: (i)
The historical data of degumming and neutralization unit have been analyzed;
(ii)
Experiments were conducted in the water degumming step;
(iii) Laboratory experiments of water degumming and chemical degumming and neutralization were made. In these experiments the influence of various process parameters was analyzed: (i)
On the degummed oil loss and efficiency of degumming in the case of water degumming;
(ii)
On the losses of neutral oil and the final parameters of the oil (acidity, phosphorus and soaps) in case of the degumming and neutralization unit.
It was concluded that it is advisable to install a heat exchanger for cooling the oil before water degumming, which it is anticipated to promote an income of 120.093 euros/year. The preferable investment was estimated to be 3.711 euros, by resorting to existing equipments in storage (three shell and tube heat exchangers, arranged in series with the power needed for desired oil cooling), with a "payback" time of about 1 month of operation, so this can be economically viable.
Keywords: vegetable oil, water degumming, chemical degumming, neutralization
process,
1. Introduction
alkali
neutralization Water degumming involves mixing hot water
refining unit),
(degumming
since
and
phosphatides
potentiate the formation of emulsions.
with the oil at 70 to 80ºC, followed by a
Degumming and neutralization unit allows
centrifugation step, which allows the removal of
the removal of non-hydratable phosphatides and
gums,
hydratable
free fatty acids present in the oil. The oil is
phosphatides and other impurities. This process
preheated up to 75ºC and then phosphoric acid
significantly reduces oil losses in the next
is mixed for conditioning of non-hydratable
constituted
by
water,
1
phosphatides to a hydratable form. The extent of
In a second experiment, the flow of gums
reaction is promoted for 5 minutes in a holding
was measured by collecting of these into a
tank. Then, a caustic soda solution is added
container, timing its filling time. These measures
through
the
were done for different water flows so it was
neutralization of free fatty acids. Simultaneously,
possible to see how water flow affects the flow of
hot water is added to promote phosphatides
gums. Oil samples were taken immediately after
agglomeration, which occurs after in a slow
the centrifugation for moisture analysis.
a
static
mixer,
which
allows
stirring tank for 30 minutes. The mixture is then heated and separated in a first centrifugation step. Neutral oil is obtained as light phase and “soapstock” as heavy phase, which contains phosphatides
and
soaps
formed
during
neutralization step. The neutral oil still has a high
The third experiment was very similar to the previous one, but phosphorus content was analyzed in the centrifuge samples and in a crude oil sample taken before the experiment, in order to estimate the oil losses of the process.
content of soaps, for what is performed a
Water degumming was also simulated at the
washing step by adding a solution of citric acid.
laboratory with crude oil from the facility. Different
The
kinds of trials were carried out: variation of water
soapy
wash
water
is
separated
by
centrifugation and neutral oil is vacuum dried.
quantity, variation of water type, variation of temperature and variation of time of mixture. In these trials was used a hotplate with magnetic
2. Experimental procedures
stirring Yellow Line Mag HS7, with numerical indication of speed from 0 to 6, with temperature
Several
types
of
experiments
were
performed and these require some laboratory tests of the oil:
sensor and a centrifuge Ecco. Soybean
oil
was
taken
from
water
degumming facility for these trials, with a content
•
Free fatty acids content;
of phosphorus of 522 ppm (temperature trials)
•
Moisture (by Karl-Fischer method);
and 583 ppm (remaining trials). Hot water was
•
Soap content;
•
Phosphorus content (by ICP).
added to 25g of soybean oil at 75ºC and the mixture was done for 7 minutes. The mixture was then centrifuged for 10 minutes at 2200 rpm. The degummed oil produced was analyzed for
Three experiments were performed in water
phosphorus content.
degumming facility. In the first, the process was monitored for six days. Changes in water flow
Due to impossibility of conduction trials on
were imposed and their values were recorded, as
degumming
well as the values of oil flow and degumming
parameters were analyzed using historical data
temperature,
Furthermore,
of operation and the process was simulated at
samples of crude oil before entering degumming
the laboratory. For that propose, degummed
process and dry degummed oil were taken for
soybean oil produced in the facility was used
phosphorus content analyses.
(191 ppm of phosphorus, 0,83% of free fatty
once
per
shift.
and
neutralization
unit,
its
acids and 0,16% of moisture), as well as rapeseed oil (232 ppm of phosphorus, 2,53% of
2
free
fatty
acids
and
moisture)
Besides the high temperature, other factors may
degummed at the laboratory from virgin oil stored
be detrimental to the process, such as a possible
at the facility. Each trial required 127 g of
poor contact between oil and water and addition
degummed
of water in inadequate amount.
oil
0,11%
and
of
phosphoric
acid,
agglomeration water (distilled water) and wash water solution were added according to the
Flow measurement of gums
specific consumptions of the plant. The caustic As expected, there is a relation between the
soda solution was added according to the amount of free fatty acids present in the oil plus
water added and the gums flow rate.
the excess practiced at the plant.
hotplate with magnetic stirring used on water degumming trials and with a kitchen blender Moulinex Turbomix 2. For these trials was important to know which agitation speed was
with
probe
14000L/h
950
13000L/h
900
y = 0,6601x + 667,76 R² = 0,9357
850
y = 0,6498x + 622,32 R² = 0,9118
800 750
y = 0,6604x + 537,74 R² = 1
700 250
therefore an estimation was performed using an tachometer
15000L/h
1000
possible to accomplish with these devices,
optical
16000L/h
1050 Gums flow (kg/h)
The mixture steps were made with the same
350
450
550
Water flow(kg/h)
TMO-T6
Figure 1 – Gums flow as function of water flow
Maintenance Product. The centrifugation steps were made with the same centrifuge used in water degumming trials at 2700 rpm for 10
Knowing the moisture content in degummed
minutes. On the neutral oil free fatty acids,
oil, the flow of gums in dry basis was obtained by
moisture, soap content and phosphorus content
material balance.
were evaluated. Gums flow - dry basis (kg/h)
700
3. Results and discussion
3.1. Water degumming
16000L/h 15000L/h
650
14000L/h
600
13000L/h
550
y = -0,2669x + 703,94 R² = 0,744
500 y = -0,2911x + 658,28 R² = 0,8625
450
y = -0,1756x + 532,72 R² = 1
400
Process monitoring
250
350
450
550
Water flow (kg/h)
It was found that the operating temperature
Figure 2 - Gums flow (dry basis) as function of water flow
was 98°C rather than about 75°C, as would be suited
for
this
process.
This
has
the
disadvantage of increasing the solubility of
Since the flow of gums in dry basis
phosphatides in oil, which reduces degumming
decreases as the water flow increases, it is
efficiency. Theoretically, soybean oil has about
noticeable that total losses will also decrease,
90% hydratable phosphatides and in practice
but in the absence of phosphorus data, is not
efficiencies were between 57,0 and 82,4%.
3
possible to say if that decrease is due to less oil
corresponding degummed oil had 186 ppm of
loss or due to a worse degumming.
phosphorus.
Oil losses in water degumming
Table 2 - Results from type of water, quantity of water and mixing time trials
The
same
procedure
was
made,
but Trial
Phosphorus (ppm)
1 (control)
151
2 (water from condensates)
152
3 (water from equipment 45)
149
4 (50% of the water required)
570
5 (115% of the water required)
155
6 (agitation for 30 minutes)
547
phosphorus content was evaluated.
Table 1 – Results for degumming efficiency and losses Oil
Water
Efficiency
Total loss
Oil loss
(kg/h)
(kg/h)
(%)
(%)
(%)
13500
550
79,5
4,03
1,63
13500
500
81,1
4,20
1,76
13500
450
81,8
4,25
1,79
13500
350
82,2
4,49
2,01
12600
550
80,8
3,73
1,30
12600
500
81,2
3,83
1,39
12600
450
80,7
3,88
1,45
less water than required resulted in a decrease
12600
350
78,9
4,13
1,75
of the degree of degumming, as expected. With
It appears that neither the contaminants of water from equipment 45 (oil and hexane) or the treatment compounds of water from condensates adversely affect the degumming. The addition of
agitation Table 1 show that degumming efficiency is barely affected by water flow, so losses decrease with increasing water flow. In accordance with the literature
[1]
the oil losses should be 30% of
total losses, which means 1,43 times the
for
30
minutes
the
degree
of
degumming also decreased. For temperature trials, crude soybean oil with 522 ppm of phosphorus was used. The correspondent degummed oil at the plant had 162 ppm of phosphorus.
hydratable phosphatide content. As the crude oil contained 1005 ppm of phosphorus, the total loss should be 3,88% and 1,16% of oil loss.
Table 3 - Results from temperature trials Trial
Phosphorus (ppm)
theoretically necessary, it appears that in the
7 (control – 75ºC)
108
range of flow rates tested, the greater the water
8 (98ºC)
153
Although water flows are greater than the
flow, the lower are losses of the and lower is the representativeness of oil in total losses.
Temperature is an important factor in degumming processes, as expected. A decrease
Water degumming laboratory trials
of temperature to 75°C promotes an increase in degumming efficiency of 8.6%.
For these trials crude soybean oil with 583 ppm of phosphorus was used. At the plant, the
4
3.2. Chemical degumming and neutralization
Chemical
degumming
and
neutralization
laboratory trials In
Chemical degumming and neutralization unit
order
to
have
a
good
chemical
degumming, is very important that phosphoric
operation study
acid is well dispersed in the oil, which is Process losses are a major factor to evaluate.
influenced by the rate of mixing.
They can be obtained by data of amount of oil that enters and leaves the process and by the
determined by laboratorial analyses. In addition, a theoretical expression for this kind of processes can be used, where theoretical loss is 0,3% plus
70 Phosphorus (ppm)
Wesson Loss factor, W (eq. 1 and 2) that can be
Phosphorus (ppm)
80
flows expected by planning, but also through
60 50 40 30
80 60 40 20
20
0 5000 10000 Mixing speed (rpm)
10
the sum of free fatty acids (%), phosphatides (%),
0
0 0
moisture (%) and impurities (%) of degummed oil
500
1000
1500
Soja Soybean Colza Rapeseed
Mixing speed (rpm)
[1]
. Figure 3 – Neutral oil phosphorus content as function of speed in phosphoric acid mixing. Magnetic stirring trials only (left) and including kitchen blender trial (right)
Loss (%) = 0,3+1,25W if W
